Echo suppressor



July 14,1931. H A 1,814,038

' ECHO SUPPRESSOR Filed Aug. 10, 1928 INVENTOR .I Eel 17mm ATTORNEY Patented July 14, 1 931 ence from noise currents,

' UNITED, STATES PAT ECHO SUPPRESSOR Application filed August 10, 1928'. Serial No. 293,720.

This invention relates to improvements in voice operated devices, and more particularly to. arrangements for automatically regulating the sensitivity of such devices. 11 echo suppressoris such avoice operated device well known in the art and is utilized in connection with a two-way transmission system for disabling one of the one- Way lines of such system, while transmission is taking place in the opposite direction over another of the one-way lines of the system, thereby preventing echo effects or reflected currents from being transmitted back to the transmitting end of thesystem and disturbing the speaker. For purposes of illustration, the invention will be shown in connection with an echo suppressor device. The voice opera-ted echo suppressor must be so constructed that it Will not be operated by noise currents existing on the system. Accordingly, it has been the practice to limit the sensitivity of the device by the greatest noise ever expected to be present on the line. As the line would not at all times include this maximum noise-current, it is obvious that during quiet periods, the voice operated echo suppressor would not be operating at-maximum efliciency. In order to avoid interferthe echo suppressor device of this invention is so constructed as to be normally relatively insensitive until primed by speech currents which are stronger than the maximum noise current to beexpected on the line. In other words, the fundamental idea for securing protection against noise current consists in having the echo suppressor normally withlow sensitivity so as to be unaffected by noise whenever voice currents are absent from the circuit, and to automatically. raise the sensitivity of the echo suppressor whenever voice currents apar on the circuit. This: is accomplished by ving the echo suppressordevice primed by peaks of speech which rise above the noise level. Other objects and features of the inv vention will appear more fully from the detailed description hereinafter given. Y The invention may be more fully understood from the? following description, to-

gether with theaccompanying drawings, in

taper off the Figures 1 and 2' of which istshown a cirs E NT oer! c E- JOSEPH HERMAN, or WESdFIELD, NEW JERSEY, Assre-ivoaro. am-911cm 'rELE-rrienE q AND TELEGRAPH COMPANY, A CORPORATION on NEW Yam;

cuit diagram embodying a'preferred form of the invention and a modification. thereof, re:- spectively. Similar reference charactershave been utilized to den figures of the drawings. 1

. In Fig. 1, the echo suppressor arrange ments of theinve between the one-way sections VVE' and EWV of the well known type of four-wire circuit. Each of these one-way line sections willinclude'repeat'er apparatus, such asthe ampli; fier tubes R and R. Bridged across the line IVE on the output side of tube R'is' an am The output of this ampli 6s plifierdetector A.- fier detector A will include an arrangement of echo suppressor relays whereby the line section EVV maybe disabled. Bridged across the line EWV on the output side of the tube R will be a similar. arrangementcomprising i the amplifier-detector'A and the relay arrangement for disabling line l/VE. The general operating 7 echo suppressor device are well known in the art. w The priming by the speech currents of the, echo suppre'ssorto increaselits sensitivity could, in accordance with the arrangements ote like parts in all offthe' tion are shown associated are features and. purposes .of an ofthis invention, have either one of-two characteristics. The echo suppressor priming speech and for 'aninterval ofx'tiine '80 could be maintained at maximum between peaks of after speech ceases, or couldbe allowedto be applied to the amplifier-detector ment so as to increase its'sensitivity to weak speech, or it could be applied to the-echo supchange the degree plished by this relay arrangement.

In the arrangements of Fig.- 1, the primgradually between the peaksaiof Speech; F rth'ermorc, the priming might which i controlsthe echo suppressing. relay-arrangeing is allowed totaperofl graduallybetween V peaksof speeclnand is applied to thesup pressor relay arrangement. '.':In the platefcircuit of theamplifiersd etector A are shown two polar'relays 1 and 2, and. a: biasing .circuit therefor. including the battery --B Thepolar relay 1 is made less sensitive thanthe' relay? by means of a resistance shunted across its operating winding, or by some other means. The object is to make the relay 1 sufiiciently sensitive so as to operate fairly frequently on the peaks of voice or speech currents but not sensitive enough so as to operate on noise currents.

The polar relay 2 is made as sensitive as required for effective suppression of echoes in the case of weak speech and is therefore subject to operation by noise. A fundamental requirement for this relay is that it should not be held operated continuously by the steady noise on the circuit but should be operated and released frequently. Should the relay 2 be held operated, then the sensitivity of the echo suppressor would be only that of relay 1 and it would have a fairly long hangover.

lhe operation of relay 1 by speech currents charges the priming condenser C from the negative battery B through the winding of relay 3. The charge on this condenser is then utilized by relay 2 for sup- .pressingechoes by applying it to the grid of the repeater tube R. In other words, the negative potential on the grid of tube R will be so increased by the charge on condenser C together with the potential of battery 13,, that the tube will not function. The values of R and C in the grid circuit of repeater R determine the rate of building up of the grid voltage, and, therefore, to a large extent, the operating time of the suppressor. The rate of building up must of necessity be limited so as to avoid the transmission of clicks over the circuit whenever the grid voltage is applied. The hangover time is determined by the values of C B and R in series.

Relay 3 is operated momentarily whenever relay 1 operates. Its function is to dissipate any unused charge on condenser G when ever the direction of the conversation changes from EWV to WVE. In this way, the echo suppressor relay associated with C' is made ineffective in spite of operation by noise. The apparatus associated with the amplifier-detector A is similar to that shown associated with the amplifienA and has been given similar reference characters with the added designation prime.

The manner in which the echo suppressor arrangements of Fig. 1 would function is as follows: At the beginning of the conversation, there will be no charge on either of the priming condensers C, and C, and both sides of the circuit will have their normal equivalents in spite of the operation of relays 2 and 2" by noise. Assume that speech currents are first transmitted over the WE side of the four-wire circuit; The first peak of the speech which rises above the noise level will operate relay 1 as well as relay 2 and connect the negative battery B to the priming condenser 0 and to the grid of the tube B. This will render tube R inoperative and echo suppression will begin. As long as speech continues in this direction over the circuit, relay 2 will suppress the echoes of both noise and speech currents which operate it, utilizing the charge on C for disabling the repeater R. The charge on C is maintained at a sufficiently high level by occasional operations of relay 1 by the peaks of speech.

Should the talker pasue for a while, and no reply is received in the meantime from the other end of the circuit, the suppressor will continue to suppress the echoes of noise currents. It will, however, become less and less effective in doing this since the charge on C is being dissipated. If the pause is long enough, this charge will be entirely dissipated and the echo suppressor will be inefiective.

Should a reply be received over the EW side of the system, relay 1 will be operated by the first peak of speech and will charge the priming condenser C from battery B and, in a manner similar to that heretofore described, disable the repeater R. The charging of C through the winding of relay 3 will cause a momentary operation of this relay and discharge the priming condenser G on the other half of the echo suppressor. As a result of this, the speaker has complete control of the circuit in spite of noise currents on the opposite side and can maintain this control as well as suppress the echoes due to his speech until interrupted by voice currents from the first speaker.

In the modified form of the invention shown in Fig. 2, the priming is applied to the amplifier-detector which controls the echo suppressor relay. Accordingly, separate amplifier-detectors, such as A and B, are provided for each of the relays 1 and 2. Similar reference characters have been utilized to denote like parts with respect to Fig. 1.

The operation of the arrangements of Fig. 2 are substantially similar to those of Fig. 1 heretofore described. The following distinctions are pointed out. When the armature of relay 1 is on its 8 contact, the batteries B and B which is the grid battery of amplifier-detector B, are in series. This gives a large grid voltage on the amplifier-detector B and hence low sensitivity. \Vhen peaks of speech operate relay 1, the large condenser C which has voltage of B on it, is discharged through the winding of relay 3, thereby giving the amplifier-detector B only its normal grid voltage, namely, that of battery B \Vhen relay 1 goes back to its 8 contact, battery B slowly charges condenser C through the resistance 33,, thereby gradually decreasing the sensitivity of the amplifierdetector B by increasing its grid voltage. Relay 3 has the same function as in the arrangements reviously described in connection with ig. 1. When operated momentarily by the discharge of C it connects the battery B of the other side of the echo suppressor directly to the primin condenser C instead of through resistance makin the grid voltage of the amplifier-detector i high at once,and the amplifier-detector insensitive at once. Relay 2 has the same function as in Fig. 2. However, instead of utilizing a primingcondenser for its source of grid voltage to disable the re peater R, it utilizes the battery B in series with battery B i While the invention has been disclosed in certain specific arrangements which are deemed desirable, it is understood that it is capable of embodiment in many and other widely variedforms without departing from the spirit of the of the invention, as defined by the appended claims.

What is claimed is:

1. A transmission line, an echo suppressor device associated therewith, and means con.- trolled by speech currents transmitted over said line for increasing the sensitivity of said device.

2. A transmission line comprising two oneway line sections for transmission in opposite directions, an echo suppressor device associated with said line sections comprising two relays associated with one of said line sections, one of said relays being operative by currents in said line section of any ampli tude within a relatively wide range, the other of said relays being operative only by currents in said line section of amplitude equal to or in excess of a value considerably above the lower limit of saidrange, and means un 'der the joint control of both of said relays for disabling the other of said line sections.

3. A transmisslon line comprising two one way line sections for transmisslon in opposite directions, an echo suppressor device associated with said line sections comprising two relays associated with one of said line sections, one of said relays being operative by currents in said line section of any amplitude within a relatively wide range, the other of said relays being operatively only by currents in said line section of amplitude equal to or in excess of a value considerably above the lower limit of said range, and means for causing a gradual disabling of the other of said line sections, said means being controlled by the joint operation of both of said relays.

4. A transmission line comprising two oneway line sections for transmission in opposite directions, an echo suppressor device associated with said line sections comprlsmg a relay operated by both noise and signaling currents on said line section, a relay operated only by signaling currents on said line section, and a circuit for'disabling the other of said line sections, said relays being adapted Q, thereby to complete said circuit upon their joint operation. I 5. A transmlssion line comprislng two oneway line sectionsfor transmission in opposite directions, an echo suppressor device as-' said line sections, said circuit being controlled jointly by both of said relays, and a condenser associated with said circuit for retarding the building up and-dying down of the operating voltage applied to said circuit.

6. A transmission line comprisingtwo oneway line sections for transmission in opposite directions, vacuum tube repeaters in each of said line sections, an echo suppressor device associated with said line sections comprising a relay operated by both noise and signaling currents on said line section, a relay operated onlyby signaling currents on said line section, a circuit for applying voltage to the grid of the repeater in the other of said line sections, and means controlled by both of said relays for increasing the voltage applied to said grid circuit.

In testimony whereof, I have signed my name to this specification this 9th day of August, 1928.

JOSEPH HERMAN. 

